I cannot ping any other ipv6 address from guest, including google dns 2001:4860:4860::8888/8844. (Timed out)

I cannot ping from any non-assigned ISP ipv6 address to guest. (Timed out)

ping6 from Hosts to outside is OK.

Update:

If I change Guest's gateway to 2607:beef:be:bff:ff:ff:ff:ff (Host's gateway), the guest will complain "no route to host". Even I added the static route info (route6-eth0) to the Guest, it still won't connect.

Then how did you get it to work on the host? Also it doesn't help that you obfuscated all of your addresses.
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Michael Hampton♦Dec 27 '13 at 18:31

I think the Hosting ISP has a MAC whitelist which controls what is allowed and what's not. That's all I can guess now. Sorry for the obfuscated IPs. I am looking for another way to achieve the same purpose, possibly using virbr0 NAT. I will open another topic if problems occur. I will use true ipv6 address in my next questions.
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hlx98007Dec 27 '13 at 21:23